I configured it for both Verizon and ATT, and none work. I did enable WiFi calling on my cell, and I see it using Wifi,
but the logs show nothing.
As long as your phone has WiFi connection and can reach the ePDG gateway of ISP, VoWiFi should work.
Options given in controller is just to make experience better and smooth, but if WiFi calling is not working at all, you may have to troubleshoot further or open a support case.
Packet capture on APs eth interface will help why calling is not working.
Once you enable WiFi calling on your phone, it sends a DNS request to ISP's ePDG gateway, if DNS is not resolved, feature will not work.
If DNS is resolved, your phone will establish a ISAKMP tunnel with ISP's gateway and start sending ESP encapsulated voice traffic to the gateway.
If you are interested in in-depth troubleshooting, below is the connection flow of VoWiFi.
Client DNS query to epdg gateway, such as "epdg.epc.mnc002.mcc262.pub.3gppnetwork.org" or depending upon client's Telco it could be different name ending with .3gppnetwork.org>> DNS response >> ISAKMP Init request >> ISAKMP responder response >> Auth Init request >> Auth response >> data traffic as ESP (Encapsulating Security Payload).
@syamantak_omer Thank you for the detailed answer. Yes, I was looking to boost the priority of the Voice traffic since the cell signal at my home is low and I am forced to use wifi calling. However, each time I use wifi calling the call quality is intermittent, basically I can hear the person fine but when I talk some of the words are cut out.
My answer was completely focused on the condition that VoWiFi is not working at all.
Now if you are saying that calling is working but performance is not good, packet captures on WiFi interface and on ethernet interface will help.
Open a support case and support should be able to check the controller config and other stuff to make sure WiFi connection is good or not and why calling is not working smoothly.